To generate a favorable climate in a room large area illumination devices are needed. Nowadays often gas discharge lamps are used to generate a homogeneous light, illuminating large parts of the room. Unfortunately, discharge lamps are known to be costly and quite inefficient. To overcome this disadvantage, the use of organic light emitting diodes (OLED) is appropriate. The advantage of the OLED is that it is a homogeneous light source with potentially low costs and high efficiency. Organic light emitting devices (materials and structures) are known in the art, for instant as disclosed in WO2005/053053 A1, the disclosure of which is incorporated herein by reference for all purposes.
However, OLEDs possess a lamberic characteristic so that the light is evenly spread in all directions. This has the disadvantage that OLEDs, being used as large area illumination devices will glare. As OLEDs nowadays reach high light fluxes, the emitted artificial light will blind the eyes of a person, entering a room, being illuminated by an OLED.
In the US 2005/0259198 A1 a collimating device and a transflector for use in a system having a backlight is disclosed. The collimating device has a cone like cross-section and is embedded in an optical element layer covering the substrate of an OLED. The aim of this optical element layer is to reduce the given angular distribution of the light and to increase the peak intensity. However, the shown microscopic structure will not prevent glare, if the OLED is used as a large area illumination device.